Pb = 9
Kr = 28
Further explanation
Proust stated the Comparative Law that compounds are formed from elements with the same Mass Comparison so that the compound has a fixed composition of elements
In the same compound, although from different sources and formed by different processes, it will still have the same composition/comparison
Compounds can be formed from several elements, which can be the same or not .
The composition of the constituent elements is usually expressed in subscript
For compound : Pb₉(Al₅Kr₇)₄
The number of Pb atoms = 9
The number of Kr atoms = 7 x 4 = 28